Dielectric supported positionable inductive tuner for resonators



May13,1969 N. M.BANES ETAL 3,444,486

DIELECTRIC SUPPORTED POSITIONABLE INDUCTIVE TUNER FOR RESONATORS FiledDec. 13, 1966 FIG.1.

INVENTORS NATHAN M. BANESfl/R. JOHN D. FEEHAN BY/FAYMOND M. STEPURAATTORNEY 3,444,486 DIELECTRIC SUPPORTED POSITIONABLE INDUCTIVE TUNER FORRESONATORS Nathan M. Banes, John D. Feehan, and Raymond M.

Stepura, Gainesville, Fla., assignors to Sperry Rand Corporation, acorporation of Delaware Filed Dec. 13, 1966, Ser. No. 601,476

Int. Cl. H01p 7/06 U.S. Cl. 33383 4 Claims ABSTRACT OF THE DISCLOSURE Aturnable resonant cavity equipped with a longitudinally extensivedielectric tuning probe, one end portion of which is covered with aconductive material. The probe is variably inserted longitudinally intothe resonant cavity to adjust the frequency thereof by varying thepenetration of the conductive portion of the probe into the cavitymagnetic field. Solely the uncovered dielectric portion of the probeslidably engages the cavity wall through which insertion is made.

The present invention generally relates to inductive tuners for cavityresonators and, more particularly, to a positionable inductive tunerrequiring no sliding electrical contacts.

The use of a conductive rod or a dielectric slug for tuning cavityresonators is Well known in the art. Conductive rod tuning of a resonantcavity is accomplished by varying the penetration of the rod into themagnetic field of the cavity which in turn varies the inductance andchanges the resonant frequency of the cavity. Such conductive rod tuningis not well suited for varying the resonant frequency of the cavity overa wide range. Wide range tuning involves substantial amounts of rodtranslation and requires the use of sliding electrical contacts in orderto maintain electrical continuity between the inductive rod and thecavity walls over the full range of translation. Sliding electricalcontacts are diflicult to fabricate and tend to become unreliable withextended use.

In the case of a dielectric slug, the resonant frequency of the cavityis changed by varying the penetration of the slug into the electricfield of the cavity thereby presenting a variable capacitance. Althoughthe requirement of sliding electrical contacts is eliminated when adielectric slug is utilized, a new problem arises if vaporized metal ispresent in the vicinity of the dielectric slug. Such a condition exists,for example, where there is high density electron beam bombardment ofgrids in a reentrant cavity reflex klystron which causes vaporized metalto evolve from the grids. Vaporized metal tends to deposit on the coolerportions of the klystron interior, including the dielectric slug. Themetal deposited on the dielectric slug provides a highly resistive pathfor the flow of current across the surface of the dielectric. Thisresults in a lowering of the cavity Q which, in turn, lowers poweroutput and efficiency.

Thus, the conductive rod technique is handicapped by the need forsliding electrical contacts whereas the dielectric slug scheme suffersfrom reduced cavity Q in the presence of vaporized metal,

One object of the present invention is to provide a wide frequency rangecavity tuner requiring no sliding electrical contacts while maintainingmaximum cavity Q even in the presence of vaporized metal.

Another object is to provide a wide frequency range inductive tuner fora cavity resonator requiring no sliding electrical contacts.

nited States Patent 6 ice An additional object of the invention is toprovide a wide frequency range tuner for a cavity resonator having therespective advantages but not the disadvantages of conductive rod anddielectric slug tuners.

Another object is to provide a medium power, wide frequency range tunerfor use above 10 gigahertz which does not have the severe mechanicaltolerance problem of present designs,

These and other objects of the present invention, as will appear from areading of the following specification, are accomplished by theprovision of a longitudinally extendible dielectric tuning probe, oneend portion of which is covered with a conductive material. The probe isinserted longitudinally into the resonant cavity whose frequency is tobe varied so that the probe penetrates into the region where themagnetic field predominates. The conductive cladded end of the probevaries the effective volume of the cavity, as the probe is variablyinserted or withdrawn, in the manner of a conventional conductive rodtuner. The uncladded portion of the probe has no effect upon themagnetic field but serves to guide and position the conductively claddedportion. The uncladded portion slidably engages the aperture in thecavity wall through which the tuning probe is inserted. The tuning probeis tapered to have a reduced cross-sectional area in the conductivelycladded portion to prevent physical contact between said portion and thecavity wall.

For a more complete understanding of the present invention, referenceshould be had to the following specification and to the figures ofwhich:

FIGURE 1 is a simplified cross-sectional view of the cavity tuner of thepresent invention utilized in a reentrant cavity reflex klystron; and

FIGURE 2 is a perspective view of the tuning probe utilized in theembodiment of FIGURE 1.

Referring to FIGURE 1, an electron beam represented by the dashed arrows1 is generated by a conventional electron gun (not shown) and isdirected into reentrant resonant cavity 2. The resonant frequency ofcavity 2 is determined by the distance between grids 3 and 4 and by theextent of insertion of composite tuning probe 5 through an aperture 6 inthe walls 7 of the cavity. Only the reentrant cavity portion of theklystron is depicted in the simplified drawing for the sake ofsimplicity and clarity of exposition. The detailed structure of aconventional reflex klystron is described in U.S. Patent No. 2,966,611,for Ruggedized Klystron Tuner, issued Dec. 27, 1960, in the name of L.H. Sandstrom and assigned to the present assignee.

The composite tuning probe 5 of FIGURES 1 and 2 comprises a rod ofdielectric material which is conductively clad at tapered end region 8.A ceramic material 9 such as, for example, A1 0 is suitable for use asthe dielectric material of probe 5. The dielectric material is metalizedat portion 8 by conventional plating processes, for example, by firstnickel plating and then copper plating in order to provide a highlyconductive surface on the probe end region. The reduced diameter of thetapered end 8 of probe 5 prevents physical contact between theconductive surface of the probe and the cavity wall 7. Wall 7 slidablyengages soley the larger diameter portion 9 of probe 5 which is uncladdielectric material.

Probe 5 may be variably inserted or withdrawn from cavity 2 upon thelongitudinal translation of screw 10 in a manner now to 'be described.Screw 10 engages the inner threads 14 of hollow screw 11 whose outerthreads 12 engage threaded end member 13. End member 13, after assembly,is held in place by means of set screws 15 and 16. Collar 17 threadablyengages screw 10 and maintains heldical spring 18 in compression againstend member 13. Collar 17 serves as a mechanical stop to limit themaximum insertion of probe upon contact with ring 19 which is fixed tocup 20. Bellows 21, which is attached at one end to the bottom of cup20', and at the other end to screw 10, allows for the longitudinaltranslation of screw upon the rotation of screw 11. Screw 10 is rigidlyattached to probe 5.

The pitches of inner threads 14 and outer threads 12 of screw 11 aredifierentially related so that a given rotation of screw 11 causes asmall amount of longitudinal translation of screw 10 whereby theinsertion of probe 5 within cavity 2 may be closely controlled. Theadjusted longitudinal position of screw 10 and probe 5 is held fixed bycrimping the shoulder portion 23 of collar 17.

In operation, probe 5 is is inserted in cavity 2 in the region where themagnetic field predominates. The conductively cladded portion (endregion 8) of probe 5 reduces the eifective volume of cavity 2 availableto the magnetic field thereby increasing the resonant frequency ofcavity 2 in the manner of a conventional all-conductive probe.Conversely, the resonant frequency of cavity 2 decreases as the probe iswithdrawn from the cavity in a. direction away from the gap betweengrids 3 and 4. The uncladded dielectric portion of probe 5 serves tosupport the conductively cladded end region 8 at an adjustable positionwithin cavity 2 to permit the adjustment of the cavity resonantfrequency. The tapering of the end region 8 prevents physical contactwith the cavity wall 7 and eliminates the requirement of slidingconductive contacts between probe 5 and cavity wall 7. Such physicalcontact is restricted to the uncladded dielectric portion of probe 5 inthe manner of conventional all-dielectric probe tuners. Thus, thecomposite conductive and dielectric tuning probe of the presentinvention is characterized by the respective advantages of prior artinductive and dielectric tuners without suffering the disadvantagesthereof.

While the invention has been described in its preferred embodiments, itis to be understood that the words which have been used are words ofdescription rather than limitation and the changes within the purview ofthe appended claims may be made without departing from the true scopeand spirit of the invention in its broader aspects.

What is claimed is:

1. A tunable resonant cavity having a passage extending through a wallthereof and communicating through an aperture with the interior of saidcavity through which a longitudinally extendible probe is inserted,

the resonant frequency of said cavity being determined by the amount ofpenetration of said probe in said cavity, said probe comprising alongitudinally extending member slidably fitted within said passage insliding contact with the walls thereof to be guided and positionedthereby,

the surface of one end portion of said member being dielectric materialand the surface of the other end portion of said member beingelectrically conductive material, and

means for variably inserting said probe through said aperture and intosaid cavity so that only said dielectric material contacts the cavitywall surrounding said aperture and so that varying amounts of said otherend portion of said member pentrates into the region of said cavitywhere the magnetic field predominates.

2. A cavity as defined in claim 1 wherein said probe comprises adielectric material and the surface of said other end portion is coveredwith an electrically conductive material.

3. A cavity as defined in claim 1 wherein said other end portion of saidprobe is shaped so as to avoid physical contact with the walls of saidcavity.

4. A cavity as defined in claim 1 wherein said other end portion of saidprobe is tapered to have a reduced cross-section relative to that ofsaid one end portion.

References Cited UNITED STATES PATENTS 3,013,230 12/1961 Simkovich 33-833,308,402 3/1967 Grande 33-83 FOREIGN PATENTS 307,494 8/ 1955Switzerland.

HERMAN K. SAALBACH, Primary Examiner.

L. ALLAHUT, Assistant Examiner.

US. Cl. X.R. 315-5 .53

